#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <assert.h>
#define IOS ios::sync_with_stdio(false)
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;


#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <bitset>
int dp[2][2];
void work() {
    int n;
    scanf("%d", &n);
    int x;
    scanf("%d", &x);
    int pre = x;
    int now = 0;
    for (int i = 2; i <= n; ++i) {
        scanf("%d", &x);
        now = !now;
        dp[now][0] = dp[!now][1] + abs(1 - pre);
        dp[now][0] = max(dp[now][0], dp[!now][0] + 1 - 1);

        dp[now][1] = dp[!now][1] + abs(x - pre);
        dp[now][1] = max(dp[now][1], dp[!now][0] + x - 1);
        pre = x;
    }
    cout << max(dp[now][0], dp[now][1]) << endl;
}

int main() {
#ifdef local
    freopen("data.txt", "r", stdin);
//    freopen("data.txt", "w", stdout);
#endif
    work();
    return 0;
}